Ionic functionalization of aromatic polymers for ion exchange membranes

ABSTRACT

The electrochemical energy conversion system of the present disclosure includes an anode, a cathode, and an ion exchange membrane including a polymer having an aromatic polymer chain and an alkylated substrate including an alkyl chain, and at least one ionic group. The alkylated substrate is bound to at least one aromatic group in the polymer chain via Friedel-Crafts alkylation of the at least one aromatic group. The alkylation reaction utilizes a haloalkylated tertiary alcohol or a haloalkylated alkene as a precursor. In the presence of an acid catalyst, a carbocation is generated in the precursor which reacts with the aromatic rings of the polymer chain. The at least one ionic group is then replaced with a desired cationic or anionic group using a substitution reaction. The membranes exhibit advantageous stability achieved through a simplified and scalable reaction scheme.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under grant nos. 1534289and 1506245 awarded by the National Science Foundation, and grant nos.DE-AR0000769, DE-AC52-06NA25396 and A30636 awarded by the Department ofEnergy. The government has certain rights in the invention.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in its entirety and for all purposes.

BACKGROUND

Recently anion exchange membrane (AEM) fuel cells have gained asignificant interest because of faster kinetics of oxygen reductionreaction and the possibility to use nonprecious metal forelectrocatalysts in alkaline operating condition compared to acidicproton exchange membrane fuel cells. Unfortunately, these potentialbenefits have not been realized in long-lived fuel cell devices becauseof the drawbacks of currently available AEMs, which include poorchemical stability in alkaline operating conditions, insufficientmechanical stability, low hydroxide conductivity, and the lack ofconvenient synthetic methods for rapid synthesis of these materials.

A focus of AEM research has been synthesis of anionic polymer membraneswith long-term alkaline stability and high hydroxide conductivity. Thedurability of AEMs is heavily dependent on the chemical stability ofpolymer backbone. For example, poly(arylene ether)s, the most commonbackbone structure of AEMs, contain aryl ether linkages and the backboneis prone to undergo chain scission in alkaline conditions by thenucleophilic attack of the hydroxide ion, significantly reducing the AEMdurability. Due to good chemical stability of backbone in alkalinecondition, elastic mechanical property, nanoscale phase separationmorphology, and commercial availability,polystyrene-£-poly(ethylene-co-butylene)-£-polystyrene (SEBS) can serveas a promising candidate for preparation of AEMs.

However, when chloromethylation was attempted to introduce afunctionality to SEBS for synthesis of AEM, the polystyrene (PS) blockof SEBS has resulted in gelation or low levels of functionalization. Toovercome these limitations, functionalization of SEBS for AEMapplications based on transition metal-catalyzed C—H borylation andSuzuki coupling reactions has been attempted. However, the use ofexpensive transition metal catalysts, such as Ir and Pd, can be a majorbarrier to broader application of the reaction, particularly at scale.

SUMMARY

Some embodiments of the disclosed subject matter are directed to anelectrochemical energy conversion system including an anode, a cathode,and an ion exchange membrane disposed between the anode and the cathode.In some embodiments, the ion exchange membrane is a moisture diffusionmembrane (sometimes referred to as a pervaporation membrane). In someembodiments, the ion exchange membrane includes comprising a polymerhaving an aromatic polymer chain, an alkylated substrate including alinker, an alkyl chain, and at least one ionic group, wherein thealkylated substrate is bound to at least one aromatic group in thepolymer chain. In some embodiments, the alkylated substrate is attachedto the aromatic polymer chain via Friedel-Crafts alkylation of the atleast one aromatic group. In some embodiments, the alkylated substrateis bound by the linker to at least one aromatic group in the aromaticpolymer chain via Friedel-Crafts alkylation of the at least one aromaticgroup with a haloalkylated precursor substrate.

In some embodiments, the aromatic polymer chain includes polystyrene,polysulfone, poly(phenylene oxide), poly(phenylene), polystyrenecopolymers, polysulfone copolymers, poly(phenylene oxide) copolymers,poly(phenylene) copolymers, or combinations thereof. In someembodiments, the alkyl chain has a length of 1 to about 20 carbons. Insome embodiments, the at least one ionic group includes an alkylammoniumgroup, a sulfonate group, a phosphonate group, a carboxylate group, anamine, or an alcohol. In some embodiments, the linker is a secondary,tertiary, or quaternary carbon. In some embodiments, the haloalkylatedprecursor substrate includes a haloalkylated tertiary alcohol, ahaloalkylated alkene, or combinations thereof. In some embodiments, thehaloalkylated precursor substrate includes 7-bromo-2-methylheptan-2-ol,6-bromo-2-methylhexan-2-ol, 5-bromo-2-methylpentan-2-ol,6-bromo-1-hexene, 7-bromo-2-methyl-2-heptene, or combinations thereof.In some embodiments, the polymer includes the structure according toformula III:

wherein R3 includes H, CH₃, or (CH₂)_(n)R5, R4 includes H, CH₃, or(CH₂)_(n)R5, R5 includes at least one ionic group, n=1 to about 20, a/bis about 0.05 to about 0.5 by weight of the polymer according to formulaIII, and x=0.05 to about 0.95.

Some embodiments of the disclosed subject matter are directed to amethod of making an ion exchange membrane material including providing areaction medium including an aromatic polymer chain, a haloalkylatedprecursor substrate, and an acid catalyst, the haloalkylated precursorsubstrate including an alkyl chain and a halide group; reacting thehaloalkylated precursor substrate via Friedel-Crafts alkylation of anaromatic group in the aromatic polymer chain with the haloalkylatedprecursor substrate to attach the alkyl chain and the halide group tothe aromatic group; and performing a substitution reaction to replacethe halide group with at least one ionic group. In some embodiments, theacid catalyst includes triflic acid, trifluoroacetic acid, sulfuricacid, methanesulfonic acid, para-toluenesulfonic acid, or combinationsthereof.

In another aspect, a polymer according to formula IV, is provided.

-   -   wherein Ar is an aryl;    -   Z is selected from the group consisting of O, S, CH₂, and C₆H₄;    -   R is an alkyl;    -   FG comprises a moiety selected from the group consisting of an        alkyl, an aryl, OH, a sulfonate, a phosphonate, and a quaternary        ammonium group, wherein at least one FG comprises an ionic        moiety;    -   EW comprises a moiety selected from the group consisting of an        electron-withdrawing group, CF₃, a nitrile, an amide, a        pyridine, a heterocyclic amine, —C═O, and an amide;    -   x is from 1 to 20;    -   n and m are each independently from 100 to 1,000,000.

In some embodiments, the polymer of formula IV is an anion exchangepolymer. In some embodiments, at least one FG comprises a quaternaryammonium group. For example, at least one FG may include(CH₂)_(x)·N⁺R₁R₂R₃, wherein R₁, R₂, and R₃ is each an alkyl (e.g.,methyl). In some embodiments EW is CF₃. In some embodiments, Ar informula IV includes

or combinations thereof.

In some embodiments the polymer of formula IV has formula V:

In some embodiments, the polymer is a cation exchange polymer. In someembodiments, at least two FGs in a repeating unit include an ionicmoiety. In some embodiments, at least three FGs in a repeating unitinclude an ionic moiety.

In another aspect, a polymer according to formula VI, is provided:

wherein Ar is an aryl;R is an alkyl;EW comprises a moiety selected from the group consisting of anelectron-withdrawing group, CF₃, a nitrile, an amide, a pyridine, aheterocyclic amine, —C═O, and an amide;x is from 1 to 20;n and m are each independently from 100 to 1,000,000.

In some embodiments EW is CF₃. In some embodiments Ar in formula VIincludes

or combinations thereof.

In some embodiments the polymer of formula VI has formula VII:

In another aspect, a polymer according to formula VIII, is provided:

wherein GC is a graft chain comprising multiple ionic moieties;wherein Ar is an aryl;R is an alkyl;EW comprises a moiety selected from the group consisting of anelectron-withdrawing group, CF₃, a nitrile, an amide, a pyridine, aheterocyclic amine, —C═O, and an amide;x is from 1 to 20;n and m are each independently from 100 to 1,000,000.

In some embodiments the multiple ionic moieties include multiplequaternary ammonium groups. In some embodiments EW is CF₃. In someembodiments Ar in formula VIII includes:

or combinations thereof.

In some embodiments R is an alkyl and EW is CF₃.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show embodiments of the disclosed subject matter for thepurpose of illustrating the invention. However, it should be understoodthat the present application is not limited to the precise arrangementsand instrumentalities shown in the drawings, wherein:

FIG. 1 is a schematic drawing of an electrochemical energy conversionsystem including an ion exchange membrane according to some embodimentsof the present disclosure;

FIG. 2A is a chart of a method for making an ion exchange membraneaccording to some embodiments of the present disclosure;

FIG. 2B is a chart of a method for making an ion exchange membraneaccording to some embodiments of the present disclosure;

FIG. 2C is a chart of a method for making an ion exchange membraneaccording to some embodiments of the present disclosure:

FIG. 3 is a chart showing nuclear magnetic resonance spectra forpolystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) andpolymers according to some embodiments of the present disclosure;

FIG. 4 is a chart of measured properties representative of someexemplary polymers according to some embodiments of the presentdisclosure; and

FIG. 5 is a chart of measured properties representative of someexemplary polymers according to some embodiments of the presentdisclosure.

FIG. 6A is a chart illustrating a linear multication graft copolymeraccording to some embodiments of the present disclosure.

FIG. 6B is a chart illustrating a branched multi-ion copolymer accordingto some embodiments of the present disclosure.

FIG. 7A is a chart illustrating a linear multication graft copolymeraccording to some embodiments of the present disclosure.

FIG. 7B is a chart illustrating a branched multi-ion copolymer accordingto some embodiments of the present disclosure.

DETAILED DESCRIPTION

Referring now to FIG. 1 , aspects of the disclosed subject matterinclude an electrochemical energy conversion system 100 including ananode 110, a cathode 120, and an electrolyte 130 disposed between theanode and the cathode. System 100 is suitable for use in numerousapplications, such as fuel cells, energy recovery ventilation systems,water hydrolysis systems, electrochemical hydrogen compressors,batteries, sensors, actuators, etc. In some embodiments, anode 110 andcathode 120 are composed of any suitable material for use withelectrolyte 130 in system 100. Further, system 100 includes any suitableinlets/outlets 140 to supply reactants to and remove reaction productsfrom anode 110, cathode 120, and electrolyte 130.

In some embodiments, electrolyte 130 is a solid electrolyte. In someembodiments, electrolyte 130 is an ion exchange membrane 150. In someembodiments, ion exchange membrane 150 is an anion exchange membrane ora cation exchange membrane. In some embodiments, the ion exchangemembrane is a moisture diffusion membrane. In some embodiments, the ionexchange membrane 150 is at least in part composed of a functionalizedbase polymer. In some embodiments, the base polymer is an aromaticpolymer, e.g., a polymer chain whose structure includes aromatic rings.At least some of the aromatic polymers are functionalized with at leastone hydrocarbon chain and at least one ionic group. In some embodiments,the polymer includes the structure according to formula I:

where R1 is an aromatic polymer chain and S is at least one alkylatedsubstrate. In some embodiments, the alkylated substrate includes atleast one hydrocarbon group (Ak) and at least one ionic group (R2) asgenerally depicted in formula II:

In some embodiments, S is bound to at least one aromatic group in R1. Insome embodiments, the hydrocarbon group Ak of S is bound directly to theat least one aromatic group in R1. In some, S includes a linker which isbound directly to the at least one aromatic group in R1, as will also bediscussed in greater detail below. In some embodiments, R2 is a headgroup disposed at an end of Ak.

In some embodiments, R1 includes polystyrene, polysulfone,poly(phenylene oxide), poly(phenylene), polystyrene copolymers,polysulfone copolymers, poly(phenylene oxide) copolymers,poly(phenylene) copolymers, block copolymers including polystyrene,polysulfone, or poly(phenylene oxide), poly(phenylene), or combinationsthereof. In some embodiments, R1 includespolystyrene-b-poly(ethylene-co-butylene)-b-polystyrene. In someembodiments, R1 has a degree of functionalization between about 5% andabout 95%, i.e., between about 5% and about 95% of the aromatic groupsin R1 are functionalized with at least one S.

In some embodiments, Ak includes a hydrocarbon group having a length of1 to about 20 carbons. In some embodiments, the hydrocarbon group has alength of about 2 to about 4 carbons. In some embodiments, thehydrocarbon group is a hydrocarbon chain (branched or unbranched), ahydrocarbon ring, or combinations thereof. In some embodiments, thehydrocarbon group is fully saturated. In some embodiment, thehydrocarbon group includes at least one unsaturated carbon. In someembodiments, the hydrocarbon group is an alkyl group, e.g., an alkylchain. In some embodiments, the alkyl chain has a length of 1 to about20 carbons. In some embodiments, the alkyl chain has a length of about 2to about 4 carbons. In some embodiments, the alkyl chain has a length of3 carbons. In some embodiments, the at least one ionic group includes analkylammonium group, a sulfonate group, a phosphonate group, acarboxylate group, an amine, or an alcohol. In some embodiments, the atleast one ionic group includes two or more ionic groups. In someembodiments, the two or more ionic groups are the same. In someembodiments, the two or more ionic groups are different.

In some embodiments, the polymer includes the structure according toformula III:

where R3 includes H, CH₃, or (CH₂)_(n)R5, R4 includes H, CH₃, or(CH₂)_(n)R5, R5 includes at least one ionic group, n=1 to about 20, a/bis about 0.05 to about 0.5 by weight of the polymer according to formulaIII, and x is at least 0.05. In some embodiments, n is about 2 to about4. In some embodiments, n=3. In some embodiments, x is about 0.05 toabout 0.95. In some embodiments, x is about 0.45 to about 0.95. In someembodiments, x is about 0.7 to about 0.9. In some embodiments, x=0.8.While the aromatic groups from formula III are shown to befunctionalized at the C4 carbon, the polymers of the present disclosureare not limited in this regard, as the aromatic groups can befunctionalized at any available aromatic group carbon, e.g., the C2, C3,C5, C6, or combinations thereof. In some embodiments, ion exchangemembrane 150 is composed substantially entirely of material consistentwith the embodiments described above. In some embodiments, the materialis incorporated into or attached to a base polymeric structure, such asa commercially available membrane.

Referring now to FIG. 2A, some aspects of the disclosed subject matterinclude a method 200 of making an ion exchange membrane material. Insome embodiments, at 202, a reaction medium is provided that includes anaromatic polymer chain and a precursor substrate. In some embodiments,the precursor substrate includes at least one hydrocarbon group and atleast one ionic precursor group. As discussed above, in someembodiments, the hydrocarbon group is a hydrocarbon chain, a hydrocarbonring, or combinations thereof. In some embodiments, the hydrocarbongroup is an alkyl chain. In some embodiments, the ionic precursor groupis a halide group, i.e., a group including Br, I, C1, etc., orcombinations thereof. In some embodiments, the precursor substrateincludes a haloalkyl group, i.e., includes an alkyl group and a halidegroup, which is referred to herein as a “haloalkylated precursorsubstrate.” In some embodiments, the precursor substrate, e.g., ahaloalkylated precursor substrate, includes a reaction domain. In someembodiments, the reaction domain is configured to react with aromaticgroups in the aromatic polymer chain to incorporate the hydrocarbongroup and the ionic group into the polymer chain.

At 204, the precursor substrate, e.g., a haloalkylated precursorsubstrate, is reacted with an aromatic group in the aromatic polymerchain to attach the at least one hydrocarbon group, e.g., an alkylchain, and the at least one ionic precursor group, e.g., a halide group,to the aromatic group. In some embodiments, reaction 204 occurs betweenthe reaction domain and an aromatic group. In some embodiments, reaction204 is a Friedel-Crafts alkylation reaction. In some embodiments, thereaction domain is a tertiary alcohol. In some embodiments, the reactiondomain is an alkene. Therefore, in some embodiments, the precursorsubstrate includes a haloalkylated tertiary alcohol, a haloalkylatedalkene, or combinations thereof. In some embodiments, the precursorsubstrate includes 7-bromo-2-methylheptan-2-ol,6-bromo-2-methylhexan-2-ol, 5-bromo-2-methylpentan-2-ol,6-bromo-1-hexene, 7-bromo-2-methyl-2-heptene, or combinations thereof.

In some embodiments, the reaction medium includes an acid catalyst. Insome embodiments, the acid catalyst includes triflic acid,trifluoroacetic acid, sulfuric acid, methanesulfonic acid,para-toluenesulfonic acid, or combinations thereof. Without wishing tobe bound by theory, during the Friedel-Crafts alkylation reaction, acarbocation is generated in the precursor substrate at the reactiondomain in the presence of the acid catalysts. Referring now to FIG. 2B,for example, a haloalkylated tertiary alcohol generates a tertiarycarbocation in the presence of an acid catalyst such as triflic acid.The generated tertiary carbocation then readily reacts with a electronsof the aromatic rings of the aromatic polymer chain. The result is ahaloalkyl group from the haloalkylated tertiary alcohol bound to anaromatic ring of the aromatic polymer chain, in this case via a linker,e.g., a quaternary carbon. Referring now to FIG. 2C, for example, ahaloalkylated alkene generates either a secondary or a tertiarycarbocation in the presence of an acid catalyst such as triflic acid.The generated secondary or tertiary carbocation then readily reacts witha electrons of the aromatic rings of the aromatic polymer chain. Theresult is a haloalkyl group from the haloalkylated alkene bound to anaromatic ring of the aromatic polymer chain, in this case via a linker,e.g., a secondary, tertiary, or quaternary carbon.

As a result of reaction 204, at least some aromatic groups arefunctionalized with the hydrocarbon group having the ionic precursorgroup. At 206, in some embodiments, a substitution reaction is performedto replace the ionic precursor group with at least one ionic group. Insome embodiments, the at least one ionic group includes an alkylammoniumgroup, a sulfonate group, a phosphonate group, a carboxylate group, anamine, or an alcohol. The specific pendent chains and/or groups thatfunctionalize the aromatic groups are easily tunable by tuning theprecursor substrate and the substitute reaction reactants. For example,longer hydrocarbon groups in the precursor substrate can result in alonger tether length between the polymer chain and the at least oneionic group. Further, by adjusting the composition of the reactionmedium during substation reaction 206, method 200 can control what ionicgroups replace the precursor ionic groups, thus tuning thefunctionalization of the membrane.

The polymeric materials consistent with the embodiments of the presentdisclosure are advantageous for use as membrane materials due to theirchemical stability. The method of making these polymeric materials isadvantageously simplified through use of Friedel-Crafts alkylationreaction steps mentioned above to functionalize suitable aromaticpolymer chains in a one or two step reaction scheme, and further allowsconvenient control over alkyl tether length and ion head groups duringfunctionalization. The catalysts for use in reactions are inexpensive,and advantageously do not produce harmful, or in some cases any,byproducts.

EXAMPLE Example 1: Preparation with Haloalkylated Tertiary Alcohols

The aromatic rings ofpolystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS)(Mn=105,000 g/mol, and Mw/Mn=1.04) with 18 mol % (30 wt. %, 25 vol. %)PS block were functionalized via acid-catalyzed Friedel-Craftsbromoalkylation as discussed above with bromoalkylated tertiary alcoholsas a substrate. Without wishing to be bound by theory, as the tertiaryalcohol is protonated by a Brønsted acid, it loses water as a byproductand forms a tertiary carbocation intermediate which can readily reactwith the π electrons of the aromatic rings to generate bromoalkylatedSEBS. Slightly more than 1 eq. of acid (1.1-1.2 eq.) relative to thetert-alcohol reagent was used because the byproduct water is alsoreadily protonated by triflic acid reducing its reactivity. Excessiveaddition of triflic acid can cause gelation of the polymer. Since thereaction is exothermic, the reaction was conducted at 0° C.

To substitute the halide group, SEBS-C5-Br-0.8 (0.18 g) was dissolved intoluene (4 mL), filtered, and cast onto a glass plate. The drySEBS-C5-Br-0.8 film (approximately 40 μm thick) was immersed in aqueoustrimethylamine (45 wt % in water) at 45° C. for 48 h. The film wasrinsed with water and ion exchanged to hydroxide form by immersing in 1MNaOH at room temperature for 48 h in an argon-filled glovebox.

The degree of functionalization (DF) of the PS block was controlled bychanging the molar ratio of the tert-alcohol reagent to aromatic ring ofthe PS block. For example, a reaction with 0.5 eq. of the bromoalkylatedtert-alcohol relative to PS block resulted in 50 mol % DF while areaction with 1.0 eq. of the alcohol reagent resulted in 80 mol % DF. 95mol % DF could be achieved for the PS block of SEBS when 2.0 eq. of thetert-alcohol was employed, however, the resulting quaternary ammonium(QA) membrane after the amination step (i.e. SEBS-C5-TMA-0.95) exhibitedinstability. SEBS is a thermoplastic elastomer comprised of a softpoly(ethylene-co-butylene) (PEB) block and a hard PS block. Withoutwishing to be bound by theory, after incorporation of QA groups into thePS block, the water molecules absorbed in the PS block acted as aplasticizer to soften the hard block, resulting in the membrane withincreased swelling and reduced mechanical strength. Thus, some balancebetween ion exchange capacity (IEC) and mechanical properties isdesirable.

DFs were calculated by comparing proton integration values of the 1H NMRspectra. Referring now to FIG. 3 , in the 1H NMR spectrum of pristineSEBS, the integration ratio of Ar—H₅ (peaks a₁₋₃ at 6.3-7.2 ppm),butylene-CH₃ (peak c at 0.7-0.9 ppm), and the other CH₂ and CH (peak bat 1.0-2.0 ppm) indicates that the molar ratios of styrene, ethylene,and butylene contents are 18 mol %, 51 mol % and 31 mol %, respectively.After Friedel-Crafts reaction with bromoalkylated alcohols, new protonsignals of —CH₂Br at 3.2-3.3 ppm (peak d) along with the —CH₂CH₂Brsignal (peak e) appeared. DFs were calculated from the integration ratioof the —CH₂Br signal of the functionalized SEBS (peak d) and thebutylene-CH₃ signal of the pristine SEBS (peak c).

The tether length between the cation head group and the polymer backbonewas controlled by modifying the alkyl chain length in the structure ofbrominated tert-alcohol. Referring now to FIG. 4 , a series ofbromoalkylated SEBSs with different tether lengths (n=3-5) and differentDFs (50 and 80 mol % of PS block) were synthesized. NMR based IECs areexpected values of OH⁻ form calculated from the concentrations ofbromoalkyl group in 1H NMR spectrum of SEBS-Cn-Br-x. Titration IECsvalues of SEBS-Cn-TMA-x were from Mohr titration method (average of twoexperiments). Water uptake was measured at room temperature in OH⁻ form(average of two measurements). Swelling was measured at room temperaturein OH⁻ form. OH⁻ σ were measured in water under argon atmosphere.

After amination of bromoalkyl side chains of SEBS-Cn-Br-x with trimethylamine, the TMA-functionalized polymers, solubility became an issue.Therefore, films of SEBS-Cn-Br-x were cast from a 5 wt. % toluenesolution on a glass plate (membrane thickness: 40-50 μm), and subsequentamination was performed by immersing the membranes in an aqueoustrimethylamine solution. Completion of the reaction was confirmed bytitrated IEC and infrared spectroscopy. The SEBS-Cn-TMA-x membranes wereflexible, elastomeric, colorless and transparent.

Example 2: Preparation with Haloalkylated Alkenes

Related to the Friedel-Crafts reaction from bromoalkylated tertiaryalcohols and SEBS from Example 1, but without wishing to be bound bytheory, similar carbocation intermediates could be formed by protonationof an alkene. Unlike the case of alcohol substrates where released waterbyproduct can be protonated by triflic acid, no such byproduct isgenerated from the reaction with alkene substrates. Thus, less amount oftriflic acid catalyst was used. For example, while 1.1-1.2 equivalentamount of triflic acid was used for the bromoalkylation with alcoholsubstrates in Example 1, 0.33 equivalent amount of triflic acid was usedto induce the bromoalkylation reaction of alkene reagents.

6-bromo-1-hexene and 7-bromo-2-methyl-2-heptene were evaluated for theFriedel-Crafts bromoalkylation with SEBS. DF was controlled by adjustingthe amount of bromoalkenes similar to the reaction with tert-alcohol. Asprotonation of 7-bromo-2-methyl-2-heptene would form the tertiarycarbocation intermediate generated from 7-bromo-2-methyl-2-heptanol, itresulted in the same QA SEBS after amination with TMA. However, withoutwishing to be bound by theory, the protonation of 6-bromo-1-hexenegenerates a secondary carbocation at C2 initially, which can rearrangeto form another secondary carbocation at C3. Thus, a mixture of C2- andC3-tethered bromoalkyl chains was attached to SEBS from the reactionwith 6-bromo-1-hexene. Referring now to FIG. 5 , following treatment bytrimethylamine, the resulting QA polymer (e.g. SEBS-en-TMA-0.8) showed atitrated IEC that agrees well with NMR based IECs from the DF. MR basedIECs are expected values of OH⁻ form calculated from the concentrationsof bromoalkyl group in 1H MR spectrum of SEBS-Cn-Br-x. Titration IECsvalues of SEBS-Cn-TMA-x were from Mohr titration method (average of twoexperiments). Since a variety of bromoalkenes are commercially availableor readily obtainable, this polymer functionalization methodology can beadopted to create different structures of QA-tethered aromatic polymersin an atom-economic synthesis without generating byproducts.

Other Embodiments

Referring now to FIGS. 6A-7B, some embodiments of the present disclosureare directed to ion exchange membranes composed of one or more polymers.In some embodiments, the one or more polymers include a polymericbackbone with one or more ions and/or ionic groups, e.g., in one or moreside chains along the backbone. In some embodiments, the polymericbackbone includes one or more polyarylenes. In some embodiments, thesecationic and anion exchange membranes (CEM and AEM, respectively)polymers do not have ether linkages (—O—) in the polymer main-chain. Insome embodiments, one or more multi-ion groups are incorporated onto thepolymer side chains. In some embodiments, the side chains include one ormore alkyl groups. In some embodiments, the polymer includes linear sidechains, branched side chains, or both linear side chains and branchedside chains. Specifically referring to FIGS. 6A and 7A, a linearmultication graft copolymer consistent with some embodiments of thepresent disclosure is shown. Specifically referring to FIGS. 6B and 7B,a branched multi-ion copolymer (cation and anion) consistent with someembodiments of the present disclosure is shown. In some embodiments, theside chains are about the same length as the polymer backbone.

In some embodiments, the polyarylenes are produced via frompolycondensation reactions of aromatic compounds and trifluoroalkylketones using strong acid, e.g., trifluorosulfonic acid (TFSA).

Methods and systems of the present disclosure are advantageous toprovide better performing ion-exchange membranes for a wide variety ofuses, e.g., alkaline exchange membrane fuel cells, alkaline exchangemembrane electrolysis, actuator, battery, and other electrochemicalenergy conversion/storage applications, water purification. Becauseionic groups are clustered in the membrane structure, these ion exchangepolymers are expected to provide better transport of ions viaionic-water channels and better stability in alkaline conditions.Further, a wide variety of ionic groups can be incorporated into theether-free backbone polymers. Finally, the polymers of the presentdisclosure overcome the alkaline stability issue of AEMs by stabilizingthe polymer structure and incorporating more robust cationic groups.

In another aspect, a polymer according to formula IV, is provided.

wherein Ar is an aryl;Z is selected from the group consisting of O, S, CH₂, and C₆H₄;R is an alkyl;FG comprises a moiety selected from the group consisting of an alkyl, anaryl, OH, a sulfonate, a phosphonate, and a quaternary ammonium group,wherein at least one FG comprises an ionic moiety;EW comprises a moiety selected from the group consisting of anelectron-withdrawing group, CF₃, a nitrile, an amide, a pyridine, aheterocyclic amine, —C═O, and an amide;x is from 1 to 20;n and m are each independently from 100 to 1,000,000.

In some embodiments, the polymer of formula IV is an anion exchangepolymer. In some embodiments, at least one FG comprises a quaternaryammonium group. For example, at least one FG may include(CH₂)_(x)·N⁺R₁R₂R₃, wherein R₁, R₂, and R₃ is each an alkyl (e.g.,methyl). In some embodiments EW is CF₃. In some embodiments, Ar informula IV includes

or combinations thereof.

In some embodiments the polymer of formula IV has formula V:

In some embodiments, the polymer is a cation exchange polymer. In someembodiments, at least two FGs in a repeating unit include an ionicmoiety. In some embodiments, at least three FGs in a repeating unitinclude an ionic moiety.

In another aspect, a polymer according to formula VI, is provided:

wherein Ar is an aryl;R is an alkyl;EW comprises a moiety selected from the group consisting of anelectron-withdrawing group, CF₃, a nitrile, an amide, a pyridine, aheterocyclic amine, —C═O, and an amide;x is from 1 to 20;n and m are each independently from 100 to 1,000,000.

In some embodiments EW is CF₃. In some embodiments Ar in formula VIincludes

or combinations thereof.

In some embodiments the polymer of formula VI has formula VII:

In another aspect, a polymer according to formula VIII, is provided:

wherein GC is a graft chain comprising multiple ionic moieties;wherein Ar is an aryl;R is an alkyl;EW comprises a moiety selected from the group consisting of anelectron-withdrawing group, CF₃, a nitrile, an amide, a pyridine, aheterocyclic amine, —C═O, and an amide;x is from 1 to 20;n and m are each independently from 100 to 1,000,000.

In some embodiments the multiple ionic moieties include multiplequaternary ammonium groups. In some embodiments EW is CF₃. In someembodiments Ar in formula VIII includes:

or combinations thereof.

In some embodiments R is an alkyl and EW is CF₃.

Although the disclosed subject matter has been described and illustratedwith respect to embodiments thereof, it should be understood by thoseskilled in the art that features of the disclosed embodiments can becombined, rearranged, etc., to produce additional embodiments within thescope of the invention, and that various other changes, omissions, andadditions may be made therein and thereto, without parting from thespirit and scope of the present invention.

What is claimed is:
 1. A polymer according to formula IV:

wherein Ar is an aryl; Z is selected from the group consisting of O, S,CH₂, and C₆H₄; R is an alkyl; FG comprises a moiety selected from thegroup consisting of an alkyl, an aryl, OH, a sulfonate, a phosphonate,and a quaternary ammonium group, wherein at least one FG comprises anionic moiety; EW comprises a moiety selected from the group consistingof an electron-withdrawing group, CF₃, a nitrile, a pyridine, aheterocyclic amine, —C═O, and an amide; x is from 1 to 20; n and m areeach independently from 100 to 1,000,000.
 2. The polymer of claim 1,wherein the polymer is an anion exchange polymer.
 3. The polymer ofclaim 1, wherein at least one FG comprises a quaternary ammonium group.4. The polymer of claim 1, wherein at least one FG comprises(CH₂)_(x)·N⁺R₁R₂R₃, wherein R₁, R₂, and R₃ is each an alkyl.
 5. Thepolymer of claim 4, wherein R₁, R₂, and R₃ is each methyl.
 6. Thepolymer of claim 4, wherein EW is CF₃.
 7. The polymer of claim 1,wherein Ar includes

or combinations thereof.
 8. The polymer of claim 1, wherein the polymerhas formula V


9. The polymer of claim 1, wherein the polymer is a cation exchangepolymer.
 10. The polymer of claim 1, wherein at least two FGs in arepeating unit comprise an ionic moiety.
 11. The polymer of claim 1,wherein at least three FGs in a repeating unit comprise an ionic moiety.12. A polymer according to formula VI:

wherein Ar is an aryl; R is an alkyl; EW comprises a moiety selectedfrom the group consisting of an electron-withdrawing group, CF₃, anitrile, a pyridine, a heterocyclic amine, —C═O, and an amide; x is from2 to 20; n and m are each independently from 100 to 1,000,000.
 13. Thepolymer of claim 12, wherein EW is CF₃.
 14. The polymer of claim 12,wherein Ar includes

or combinations thereof.
 15. The polymer of claim 12, wherein thepolymer has formula VII:


16. A polymer according to formula VIII

wherein GC is a graft chain comprising multiple ionic moieties; whereinAr is an aryl; R is an alkyl; EW comprises a moiety selected from thegroup consisting of an electron-withdrawing group, CF₃, a nitrile, apyridine, a heterocyclic amine, —C═O, and an amide; n and m are eachindependently from 100 to 1,000,000.
 17. The polymer of claim 16,wherein the multiple ionic moieties include multiple quaternary ammoniumgroups.
 18. The polymer of claim 16, wherein EW is CF₃.
 19. The polymerof claim 16, wherein Ar includes

or combinations thereof.
 20. The polymer of claim 16, wherein R is analkyl and EW is CF₃.